This invention relates generally to a shock absorber of the hydraulic-pneumatic type, and more particularly to such a shock absorber having a stationary anti-splash device frictionally held in place against the inner surface of the shock absorber casing but being displaceable only upon application of a force which exceeds that created by movement of the hydraulic damping medium during reciprocation of the piston.
Shock absorbers of the hydraulic-pneumatic type, as generally disclosed in my prior U.S. Pat. Nos. 2,721,074, 2,774,446 and 2,823,915, are primarily adapted for use in connection with vehicle wheel suspensions. These shock absorbers include a cylindrical casing closed at both ends and containing a liquid damping medium as well as a compressed gas. A piston having valve controlled passages is reciprocable in the casing via a piston rod extending from the piston outwardly through a packed opening in one of the ends. The free end of the piston rod and the opposite end of the casing have means thereon for connecting the shock absorber to the vehicle chassis and to the wheel or axle mounting of the vehicle. The casing of a shock absorber of this type is partially filled with a hydraulic liquid so as to make provision for containing a quantity of compressible gaseous fluid. One of the problems during operation of a shock absorber of the general type described herein occurs during the turbulence which takes place in the hydraulic liquid during piston reciprocation, which turbulence leads to the formation of an oil-gas emulsion which is harmful to the proper operation of the shock absorber.
The formation of such oil-gas emulsions have in the past been avoided by the provision of a floating piston in the shock absorber casing for separating the hydraulic liquid and the gaseous fluid. The shock absorber could thus be utilized with its piston rod extending outwardly either upwardly of the casing or downwardly thereof. However, shock absorbers of such type having a floating separating piston are expensive to manufacture and require extreme care in the assembly thereof. Moreover, such floating-piston shock absorbers are known to experience frequent breakdowns during their operation. And, the shock absorber casing must have an almost perfectly smooth inner surface since the slightest imperfection thereon will define a passage allowing gas molecules to pass into the oil. A high quality shock absorber casing is therefore required to be manufactured which only further increases the cost thereof.
In the aforementioned U.S. Pat. No. 2,823,915, the entirety of which is specifically incorporated herein by reference, the formation of an oil-gas emulsion is minimized by the provision of a perforated partition fixedly mounted to the inner surface of the casing at the upper portion thereof below the level of the liquid damping medium. Such a fixed partition functions as an anti-splash device which produces broken or interrupted jets, thus breaking up the mixture of oil and air during the turbulent movement of oil passing upwardly through the piston passages.
However, the partition must be disposed at a sufficiently low level below that of the oil for satisfactory operation insuring against the formation of an oil-gas emulsion. Thus, for a predetermined overall length of the shock absorber, the length of the piston stroke may need to be reduced so as to avoid any interference between the piston and the fixed partition. This may become a serious inconvenience. Otherwise the shock absorber would need to be lengthened to accommodate a predetermined piston stroke.